1. Field of the Invention
This invention relates to a fuel vapor emission system, and more particularly to a fuel vapor emission system suitable for a fuel injection system.
2. Description of Related Art
A typical fuel injection system for an internal combustion engine has a fuel tank, a low-pressure fuel pump, a fuel vapor separator, a high-pressure fuel pump, a fuel injector and an injection control device. The low-pressure fuel pump delivers fuel from the fuel tank to the fuel vapor separator through a first delivery passage under a relatively low pressure. The high pressure fuel pump, in turn, delivers the fuel that has been delivered to the vapor separator further to the fuel injector through a second delivery passage under a relatively high pressure. The fuel injector sprays the fuel into an air induction system of the engine or directly to a combustion chamber of the engine, under control of the injection control device. Excess fuel returns to the vapor separator through a return passage.
The vapor separator is installed in this system for separating fuel vapors, which can be produced in the first delivery passage, from the liquid fuel. Without such a vapor separator, the vapors can mixed with the sprayed fuel and vary an air/fuel ratio thereof, despite the operation of the fuel injection control device, thus causing undesirable or poor engine performance.
The fuel vapors accumulate in a space defined above the liquid fuel within the vapor separator. Conventionally, a vent is provided atop the vapor separator and this vent is normally coupled with a plenum chamber of the air induction system so as to introduce the vapors into the combustion chamber with the air to be burned therein. In some engines, the vent is connected to an exhaust manifold of an exhaust system so as to burn off the fuel vapors by the heat of exhaust gases. For example, U.S. Pat. No. 5,653,103 discloses such conventional arrangements.
A problem arises when an engine is restarted immediately after a relatively long period of operation, and in particular, continuous high speed and/or high load operation. During such operation, not only the engine, but peripheral devices and units including the vapor separator, absorb or generate intense heat therein. That is, with regard to the vapor separator, a temperature of the liquid fuel rises and hence the fuel becomes likely to produce a large amount of fuel vapors that accumulate in the space above the liquid fuel.
When the engine is restarted under such circumstances, the high-pressure fuel pump supplies the fuel to the fuel injector and excess fuel, which has been pressurized by the high-pressure fuel pump, returns to the vapor separator. The return fuel is, thus, abruptly depressurized on its way to the vapor separator and expedites the production of the fuel vapors in the vapor separator. The higher the temperature of the return fuel, the more vapors are produced.
If the vent of the vapor separator is directly connected to the air induction system as noted above, the vapors will be added onto a fuel charge that has been measured by the injection control device and shifts the air/fuel ratio to a rich side. This shift of the air/fuel ratio, for example, causes an engine stall and makes it difficult to start the engine again.
Some of the foregoing arrangements in U.S. Pat. No. 5,653,103, therefore, include a fuel vapor reduction canister in a vapor path that couples the vapor separator with the air induction system. The canister is, however, a relatively costly and cumbersome.
A need therefore exists for an improved fuel vapor emission system that can remove vapors from a vapor separator so as to prevent an engine from stalling or causing other undesirable performance without the need for a canister or other special devices.
Another need also exists for an improved fuel vapor system that can remove heat from excess fuel before returning to a vapor separator.
A marine propulsion system such as an outboard motor can of course employ the foregoing engine. Outboard motors normally includes a drive unit having an engine and a bracket assembly that is mounted on an associated watercraft. The drive unit is coupled to the bracket assembly for pivotal movement about a tilt axis so that the drive unit is tiltable relative to the watercraft. Because of this peculiar nature of the outboard motor, another problem arises with the engine disposed on the drive unit. That is, with the pivotal movement of the drive unit, the engine also pivots and the liquid fuel in the vapor separator can close the vent provided atop thereof. The vapors under this condition, therefore, cannot flow out from the vapor separator, or the liquid fuel itself, rather than the vapors, may flow out to the air induction system. Both of these situations apparently give rise to undesirable engine performance.
A need therefore exists for an improved fuel vapor emission system that allows vapors in a vapor separator to flow reliably escape and/or prevent liquid fuel from flowing out.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head member closes one end of the cylinder bore and defines a combustion chamber with the cylinder bore and the piston. A crankcase member closes the other end of the cylinder bore to define a crankcase in which a crankshaft is journaled for rotation. An air induction system is arranged to introduce air to the combustion chamber. A fuel supply system is arranged to supply fuel to the combustion chamber. The fuel supply system includes a fuel reservoir in which a space for fuel vapors is defined. A lubrication system is arranged to lubricate at least one of the piston and the crankshaft by lubricant oil. A ventilation system is arranged to couple the crankcase with the air induction system so as to deliver at least oil vapors in the crankcase to the air induction system. A fuel vapor passage is arranged to couple the space of the fuel reservoir with the ventilation system.
In accordance with another aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head member closes one end of the cylinder bore and defines a combustion chamber with the cylinder bore and the piston. A fuel supply system is arranged to supply fuel for combustion in the combustion chamber. The fuel supply system includes a fuel reservoir in which a space for fuel vapors is defined. A check valve mechanism is arranged to release the fuel vapors from the fuel reservoir at a pressure of the fuel vapors that is greater than a preset pressure.
In accordance with a further aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head member closes one end of the cylinder bore and defines a combustion chamber with the cylinder bore and the piston. A fuel supply system is arranged to supply fuel for combustion in the combustion chamber. The fuel supply system includes a fuel reservoir in which a space for fuel vapors is defined. A pair of separate passages extend from the fuel reservoir at respective vents spaced apart from each other. The separate passages cross each other.
In accordance with yet another aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head member closes one end of the cylinder bore and defines a combustion chamber with the cylinder bore and the piston. A fuel injector is arranged to spray fuel for combustion in the combustion chamber. A fuel reservoir is configured to contain the fuel. A fuel pump is arranged to pressurize the fuel in the fuel reservoir to the fuel injector. A fuel return passage is arranged to return excess fuel to the fuel reservoir. A heat exchanger is arranged to remove heat from the fuel flowing through the fuel return passage. The heat exchanger is mounted on the engine via a heat insulator.